Lime-silica insulation and method of making



Aug. 23, 1955 w. R. sElPT LIME-SILICA INSULATION AND METHOD OF' MAKING 8 Sheets-Shea?l l Filed July 11. 194e C20-IBD DJOE INVENTOR WILLARD R.SEIPT BY HIS ATTORNEYS www Aug. 23, 1955 w. R. sIEIFTV 2,716,070

I .IME-SILICA INSULATION AND METHOD OF MAKING Filed July ll, 1949 8 Sheets-Sheet 2 FIGZ. 4 Z5 PuLvERIzED DIATOMAcI-:Ous DRY INSULATION CRUDE F'BRE QUICK "IME sILIcA sAND EARTH wAsTE Z WATER l/ v LIME DRY OPENING HYDRATION 5/`PULVER|2ING f7 y 50 COLLECTING WATER II I I Il SCREENING MIxING INSULATING Z9 cEMENTs 52 AGITATED 55" STORAGE T SPILLAGE K MOLDv FILLING Y 55\` vIBRATION INDURATION T II 55 MOLD MOLD MOLD ,E LuaRIcATION CLEANING"- sTRIPPING 57 40 DRYING DIscARDED WASTE TRIMMING INVENTOR WILLARD R,SE|PT BY HIS ATTORNEYS 45' mmm Mmm/6W Aug. 23, 1955 w. R. sElPT LIME-SILICA INSULATION AND METHOD OF MAKING 8 Sheets-Sheena?I 3 Filed July l1. 1349 FIGS FIG.6

FIGS

INVENTOR WILLARD R. SEIFT BY HIS ,ATTORNEYS Aug. 23, 1955 w. R. sr-:lPT 2,716,070

LIME-SILICA INSULATION AND METHOD OF MAKING Filed July ll, 1949 8 Sheets-Sheet 4 FIG, 9

M I 1 7.5 7.5 10.0125 15.0 11.5 20.0 22,5 25.0 25.022521111175150 12.5 1o.o 7.5

WILLARD R. SEIPT BY HIS ATTORNEYS MM2/66M Aug. 23, 1955 w. R. sElPT 2,716,070

LIME-SILICA INSULATION AND METHOD OF MAKING WILLARD R. SEIPT BY HIS ATTORNEYS WAL/MV Aug. 23, 1955 w. R. sElPT LIME-SILICA INSULATION AND METHOD OF MAKING 8 Sheets-Sheet 6 Filed July 1l, 1949 odo or No5 .Io Jox Fl .I6

HOURS AT FULL STEAM PRESSURE www AMlx or' 52 slLlcA lOO MEAN TEMPERATURE- DEGREES FAHRENHEIT P= PERCENT BLOCKS BROKEN OR BADLY CRACKED IN SHIPPING TESTS.

| IMPACT:v FT.- LBS.

INVENTOR WLLARD R. SEIPT BY HIS ATTORNEYS DENSITYZLBS, PER CU. FT.

SOO'- Aug. 23, 1955 w. R. sElPT 2,716,070

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RATIO: IMPACT To DENSITY SQUARED INVENTOR WILLARD R. SEIPT BY HIS ATTORNEYS WMM/@haw Aug. 23, 1955 Filed July ll, 1949 RATIO'- MODULUS OF RUPTURE TO DENSITY TE MPERATURE LIMIT-DEGREES FAHRENHEIT w. R. sl-:IPT 2,716,070

LIME-SILICA INSULATION AND METHOD OF' MAKING S Sheets-Sheefl 8 FIG. 23

zooo- (D ALUNDUM IN LIME- slLrcA Mlx |900- G) CEMENT-LIME-slLlcA UME-EARTH ALUNDUM a Fe o IN LIME-slLlcA laoo- 2 3 BENTONITE 1N LIME-SIMCA lsoo- Y |300- l l l l l l l l 2 a 4 s e 1 a 9 lo PERCENT ALaoSADnt-:D To BASIC Mlx l l l 5 lo l5 2o 25 so PERCENT RECLAIM 'NVENTOR WILLARD R. SEIPT BY HIS ATTORNEYS United States Patent O 2,716,070 LIME-SILICA INSULATIGN AND METHOD OF MAKLNG Willard R. Seipt, North Wales, Pa., assigner to Keasbey and Mattison Company, Ambler, Pa., a corporation of Pennsylvania Appiication .uly 11, 1949, Serial No. 1tl4,128 2 Claims. (Cl. 10e- 126) This invention relates to an improved thermal insulation material and to the method of manufacturing such material.

One object of the invention is to provide a light weight, etlicient, high temperature insulation material of generally improved characteristics.

Another object is to provide a highly practical method of manufacturing such material.

Still another and more specic object is to provide an insulation material of the preformed type exhibiting a lesser tendency to crack from thermal warpage, and a materially higher temperature limit than the prior materials of the same type.

A further object is to provide an insulation material of the stated type which shall be less brittle than the prior materials of like type, and which, therefor, shall possess better handling characteristics.

A still further object is to provide a relatively economical insulation material of the stated type.

More particularly, the invention contemplates an insulation material of the stated type which, as compared with prior products of the same class, shall exhibit a relatively low desired density, a relatively high strength at the preferred density, a materially higher temperature limit, and above all, the ability of this low density product Ato be satisfactorily shipped and applied economically and without excess breakage.

In the attached drawings:

Fig. l shows a ow sheet illustrating diagrammatically a method and apparatus for producing insulation materials in accordance with the invention;

Fig. 2 shows a ow sheet illustrating diagrammatically a procedure for making calcium silicate insulation in accordance with the invention;

Fig. 3 is a top plan view of a type of mold that may be employed in the production of one form of the insulation materials;

Figs. 4, and 5 are, respectively, sectional views on the lines 4-4 and 5 5, Fig. 3;

Figs. 6 and 6a are front and side views, respectively, of a type of wedge inserted at the ends of the type of mold shown in Fig. 3;

Fig. 7 is an exploded view in perspective of another form of mold;

Fig. 8 is a diagrammatic representation of a preferred method of lling a mold; and

Figs. 9 to 24, inclusive, are diagrams showing graphically certain of the characteristics of insulation materials made in accordance with the invention.

Insulation materials hitherto available in commerce have exhibited unfavorable limitations in one or more important characteristics, such for example as low crushing strength, brittleness as exhibited by low resistance to mechanical shock, rapid loss of eliciency at elevated temperatures, inability to withstand high temperatures, deterioration under high humidity conditions, high trimming losses in the manufacturing process, and relatively high densities. As a result no one of these insulations is suited for all purposes, and they have been lacking in universal applicability. It is a primary object of the present invention to provide an insulation material of relatively light weight, high efficiency, high physical strength, and ability to withstand and to maintain efficiency under Patented Aug. 23, SS

high temperature conditions, which may be made by a highly practical and economical process, and which, by reason of these multiple favorable characteristics, is substantially universally applicable for thermal insulation purposes.

We have found that calcium silicate constitutes a highly favorable medium for production of insulation materials of the desired characteristics. With this material, and utilizing the basic setting reaction between lime and silica to form a hydrated calcium silicate, it is possible by practice of the present invention, to produce a molded insulation material of low material cost and involving extremely small trimming losses, wherein the density is controllable over a wide range of values extending as low as seven pounds per cubic foot. This finished product is white in color, has high strength in relation to its density, is not brittle, and has a temperature limit of about 1500 degrees Fahrenheit. In this combination of properties, the material represents a substantial improvement over the prior commercial insulation materials.

A process of manufacture of the aforesaid insulation material is illustrated diagrammatically in Fig. l of the attached drawings. As therein illustrated, asbestos libre is opened in the dry state in a mill 1, and is then blown into a cyclone 2 and dropped into a collector 3.

Pebble lime (quick-lime) is hydrated with water in a hydrator 4. The hydration is carried out with high speed agitation. The water may be either hot or cold when added to the hydrating tank. In any event, it is desirable to have the hydrated lime slurry relatively cool before it is run into a Hydrapulper 5.

To the Hydrapulper 5 is also passed the prepared iibre from the collector 3, pulverized silica sand 6, diatomaceous earth 7, and a quantity of water depending on the desired density of the product. It may be desirable also to add a small quantity of pulverized trimmings from the previous runs. After thorough mixing, the mass is transferred from the Hydrapulper to a storage tank 8. Molds 9, placed on conveyor 10, are filled from the storage tank 8 through a specially adapted filling nozzle 11, the mass preferably being leveled in the molds by any suitable means such as a scraper 12. Entrapped air is removed by shaking the molds through the medium of a suitable vibrator 13 and the molds are then placed on an autoclave car 14 and carried into an autoclave 15, where they remain under approximately pounds per square inch of steam pressure for the desired length of time, say for example, 12 hours. The molds are then removed from the autoclave and are inverted so as to strip them from the set product 16. The molds are then cleaned at 17, lubricated at 18, and returned for reuse to the conveyor 10. The stripped pieces 16 are placed in a dryer 19 and when suiciently dry are removed, trimmed and finished for shipment at 20.

In the process described above, the properly prepared asbestos fibres serve as a suspending and dispersing agent for the necessary binding materials during setting, and as a reenforcing agent in the set structure. The opened bres act also to alord a product characterized by low density and a microporous structure, relatively high strength free from brittleness, good insulating value and a high temperature limit.

It is important in the preparation of the asbestos libres as an ingredient of the thermal insulation material that the process employed shall break down the fibre bundles to a sufficient degree to yield a high bulk value in the freshly prepared slurry without excessive reduction of the original fibre lengths. I have found that a dry processing, described above in general terms and more specically hereinafter, is highly effective to this end. An other important phase of the invention, contributing to the production of the light weight thermal insulation `cause an unstable product.

being eventually removed from the molds and dried.

It is important in the production of a light weight Ythermal insulation of the hereindescribed character, having relatively high strength in relation to its light weight y anda high temperature limit, that the ingredients be proportioned so that the slurry after mixing will be mechanically stable when placed in the molds and that substantially no settling shall occur either before or during altoclaving. VIt is important also that the hydrated lime slurry be in a highly reactive form and shall be in the presence of sufficient .silica for a sufficient length of time that essentially no unreacted or Vfree lime shall remain. Too much unreacted lime tends to complete reaction of the silica is not desirable, (very fine grinding of the silica and long autoclaving times are both expensive) then a sufficient excess of silica should be added so that at least an equi-molecularrratio shall react with the lime. In such case, the interior portions of the coarser particles will not be reacted, and the unreacted YVsilica will increase the density of the product without corresponding increase in strength. YThis may be tolerated within certain limits.

fully set forth.

Y With respect to the fibre component of the thermal insulation material, it is to be noted that lime and silica require additional agents to hold them in suspension in order to produce a light weight product, that is, one with a high void content. Such suspending agents must have a high bulk value in themselves and must be compatible with lime and silica.V As set forth above, one

function of the fibres in the insulation is to disperse and Y maintain in suspension the very fine component materials until the mass has attained rigidity, to the end that the void space necessary in a light weight insulation and homogeneity of the product be maintained.y The second function of the fibres is to act as a reenforcing agent in the finished product. The greaterl the number of individual, free fibres and the greater the length to diameter ratio, the more effective will be their dispersion and suspension powers. However, the maximum reenforcing power as well as a preferred fibre orientation is obtained from a length to diameter ratio that does notexceed a certain value. For these reasons an optimum fibre preparation is highly desirable.

The present process, described in greater detail below, is calculated, therefore, to retain to as great fan extent as possible the original length of the fibres. The process is calculated also to defiberize the asbestos to as great a degree as possible, so as to increase the number of individual fibres in the slurry and yet not to exceed a critical length to diameter ratio. It is contemplated also to maintain final densities to values below 20 pounds per cubic foot and toas low as 7 pounds per cubic foot without settling, dewatering or compressing, as hereinafter fully set forth.

'Ihe process of the present invention Vwill produce an If for economic reasons,

` terial or, extensive cracking.

insulation having a uniform size of micro-pores and substantially. even distribution of said pores throughout the mass. Also, the degree of porosity or the total volume of voids may be closely controlled. A bond is obtained between the particles so that practically no shrinkage will occur on drying. The direction that the fibres assume is a function of the manner of filling the molds and'to some degree depends upon the type and preparation of the fibre. A particular fibre orientation is. essential to obtain a more flexible product that will withstand greater mechanical shock and greater warpage strains due to exposure to higher temperatures. The desired fibre alignment may be approached to a satisfactory degree by a method of filling, as hereinafter fully set forth. The temperature limit of the product of this invention is controlled by the material itself, the fibres and the fibre orientation, and temperatures of at least 1500 degrees are possible without material disintegration, excessive shrinkage or warpage, excessive softening of the yma- Tt is not understood with exactitude by what: processV the particular fibre preparation inereasesthe suspending power of the fibre, but it is possible that a combination of phenomena is responsible. The increase in number of fibres per unit weight of the original crude fibre, together with the fact that a considerable degree of original fibre length has been retained, Vundoubtedly acts to produce a meshed, fibrous network of considerably increased void space and consequently increased bulk. Furthermore, any surface contains some degree of free electrical charge so that an increase in surface area will result necessarily in an increased surface charge per unit weight. Since the fibres are reduced in diameter, the surface charges per unit weight will have increased considerably and to some extent will have approached a col-y loidal condition, or possibly colloidal in diameter but not in length. The fibres tend to iioc and itis believed that due to the repelling charges each floc lforms a bridge over the gap between two other adjacent ocs. This would leave a pore space between the fiocs. Also, each individual fibril in a fioc is held apart somewhat from its neighbors so that the ocs themselves are porous. Y The manner in which the surface charge and the mechanical nature of the fibres act together, or what other forces contribute to the vsuspending power of the fibre, is not definitely known. Whatever action is responsible, the' explanation given is not intended to limit the scope of the invention.

The amount of fibre may be varied so that the finished product contains from 8 to 40 per cent fibre on the basis of the total dry solids. It has been found that below 8 per cent fibre the suspending power is insufficient to hold the solids without appreciable settling.V Also, the reinforcing value will be reduced so that the product does not have as great a resistance to shearing and is unduly brittle. Above 40 per cent fibre the strength of the product is again reduced. The fine solids added to the fibre act as fillers between the spaces left byV the fibres, thereby reducing the pore size consideri ably, and they also act as a binder to hold the particles and the fibres in rigid interrelationship. Reduction in the amount of fine solids by increasing the fibre content will necessarily lower the bond between the fibre. Eventually the reenforcing effect of the increased fibre content is offset by the loss of bond between the fibre resulting in lower strength. Y

With respect more particularly to the character ofthe fibre component of the insulation material, I have found that the harsh asbestos fibres are preferable in that fibres of this type appear to afford better suspension' and contribute more substantially to the reinforcing function. Marsh fibres are defined as those fibres that have a greater degree of resiliency than the soft fibres; upon removal of a deiiecting force the harsh fibres more or less spring back to their original linear state whereas a soft bre will remain in a bent position upon removal of the deecting force. Harsh libres are not typical or any class of mineralogical species; there u'zay be harsh or soft Chrysotile iibres as well as harsh or soft amphiboles. While substantially any harsh bre may be used, certain grades, such for example as amosite M-l, appear to give somewhat less settling, less brittleness and the ability to withstand thermal strains to higher, hot surface temperature exposures. Other libres such as the longer grades of the C & G fibres, a harsh African chrysotile, may be used satisfactorily. For minimum density and maximum strength the fibres should be cleaned of dirt, tine stone and other foreign matter.

Fig. 2 illustrates in detail a method of manufacturing calcium silicate insulation in accordance with the invention. The raw materials, as indicated, consist of crude iibre 21, quick-lime 22, pulverized silica sand 23, diatomaceous earth 24, and dry insulation waste Z5.

The ovv sheet illustrated in Fig. 2 or" the drawings is in part a diagrammatic representation of a suitable fibre preparation process. This is.presented as an example and is not to be considered as restricting the invention. Also, the process is subject to inodiiication in detail. The screening, for example, may or may not be done, or the libres may be screened by some other method at another point in the process. An additional preparation of the iibres such as attrition of the fibres in a slurry form in any of the several attrition type mills may aiso be included in the preparation process. An example of a commercial mill that will produce satisfactory results is the Hydrapulper.

ln the procedure illustrated in Fig. 2, the crude libre is first subjected to a dry opening operation at 26. Any method of preparation is suitable as long as the crude fibres are fberized to the optimum extent so that a critical length to diameter ratio is not exceeded and so that excessive breakdown of the original fibre length does not occur. One method of accomplishing the desired result is by the use of a rotary iiberizing mill of special design. The rotor consists of a concentric ring of attached steel iingers moving in a casing of stationary fingers. The casing comprises one ring having a diameter smaller than that of the rotating ring of fingers and another having a diameter larger than that of the rotating ring. The ibre is forced through the stationary lingers by an air stream and is opened or shredded when it is struck by the rotating fingers in its passage through the two stationary rings.

As the libres come from the opening operation they pass to collectors 27. These collectors may be of the usual cyclone type familiar to the industry. From the collectors the fibres pass to screens 28 where dirt and foreign materials are removed. The cleaned fibres are then ready to be added to the mixing operation 29.

The quick-lime is hydrated with water in the hydrator tank 39. Any tank provided with suitable agitation may be used. Examples o agitation mediums are paddles, propellers or blades. The tank and the agitator should be designed so that the quick-lime is kept in suspension and is rapidly mixed with the water during the hydration. The purpose is to accomplish the hydration as quickly as possible to produce a highly colloidal hydrated lime.

The dry insulation waste 25 represents trimmings and rejected material from the iinishing operation 41. This is pulverized in a pulverizer 3l. Any type of equipment that will break up the waste so as not to pass any lumpy' material will be satisfactory. A hammermill is the preferred pulverizer. The pulverized waste may be used to a limited extent with the raw materials, as described. lt may also be bagged and sold as a light weight, high temperature insulating cement 32.

The raw materials and necessary water are run into mixer 29. Any satisfactory type of commercial mixing equipment will be suitable. The important function of the mixer is to obtain a thorough and intimate dispersion of the individual particles of the raw materials. It is important that the raw materials are thoroughly dispersed, otherwise the suspension may settle and the inished product will not attain its greatest possible physical properties as a result of the non-homogeneous structure. The result of a mix not sufficiently dispersed would tend to produce a weaker, more brittle, less efiicient insulation with a lowered temperature limit. vExamples of mixers that can be used are high speed turbo-mixers and attrition mills that can handle liquid slurries. The Hydrapulper type mixer is a commercial attrition mill having the desired action. It is important that during the mixing operation the fibres are not shortened to any appreciable extent. After the slurry is thoroughly mixed and dispersed it is transferred to the storage tank 33.

In accordance with this invention the suspended slurry is formed to shape and then allowed to set rigidly. Shaping the mass requires the use of molds, the design of which may be such that the fluid mass can be held to form until it has attained rigidity. After the material has set, it may be removed from the mold. One form of mold for blocks is a solid container of the desired dimensions with the top face open and the sides and ends tapered to facilitate removal. Such a mold is illustrated more or less diagrammatically in Figs. 3, 4, 5, 6 and 6a of the drawings. Since the mass has little if any shrinkage upon setting or drying, it is diiiicult to remove the wet block, even with tapered sides and ends. This is due in part to the retention of the piece in the mold by atmosphere pressure, since air cannot get between the mold and and the block, but the major factor in a tapered mold is due to the thermal shrinkage of the-metal mold upon cooling, which grips the encased block tightly. This condition may be remedied by inserting wedges, shown in Fig. 6 and by the broken lines in Fig. 4, in the ends with an equal but reverse taper. This not only forms a block having its ends perpendicular to the bottom of the block, but when the wedges are removed from the mold, air can enter between the block and the bottom of the mold, and the block then can very easily be separated from the mold by supporting the inverted mold and tapping it lightly. To prevent the blocks from sticking to the mold faces and particularly the bottom of the mold where the slurry had struck during the filling operation, parting compounds are used. These compounds also assist in easing the block out of the inverted mold by a lubricating action. Examples of parting compounds are petroleum oils, greases, waxes and Combinations such as paramn wax mixed with powdered mica.

Hollow elongated articles as used for pipe covering are conventionally split lengthwise to permit application to existing pipe installations. These half sections may readily be formed with a mold having a semi-cylindrical design. A length, usually slightly over 36 inches, of a smooth metal tube cut in half lengthwise or a sheet metal rolled to the proper diameter, having an inside diameter equal to the desired outside diameter of the molded material, would be suitable. Flat sheets of metal may be welded on the ends to act as retainers for the slurry and as a support to hold the mold solidly. Spacer strips of semi-circula construction are inserted at the ends of the mold. These strips are slotted to support the core concentrically within the shell of the mold, and serve also to assist in removing the mold from the set piece by eliminating binding of the mold on the piece due to thermal shrinkage. The core may also be made of a smooth metal tube or a rolled section of sheet metal with an outside diameter equal to the desired inside diameter of the molded material. Such a mold is illustrated in Fig.

7 wherein the outer mold or shell is indicated by referl ence numeral 44, the end retainers by numeral 45, the spacer strips by numeral 46 and the core by the numeral 47.

The molds are iilled with slurry by any suitable filling device, indicated at 34, the slurry being fed from the r in the molds in such a way that a preferred orientation ofthe fibre is accomplished. As explained previously the maximum reenforcing power is obtained when the fibre length to diameter ratio approaches but does not exceed a certain critical value. However, the maximum reenforcement of the fibres cannot be realized unless the. Vfibres are oriented in a preferred direction. A standard commercial size for block insulation is 36 inches long, 6 inches wide and from 1 to 4 inches thick. The greatest Ystresses will occur over the longest dimension and will causev the block to rupture through a cross section perpendicular. to the length. Hence the greatest reenforcement is vneeded to prevent this rupture. The fibre lengths should, then, be perpendicular to the above mentioned cross section or parallel to the length of the block. The preferred orientation may be obtained by one of several'ways, such as alignment by the passage of a mechanical combV through the slurry in a direction parallel to the length of the filled mold. However, I have found that the molds can be filled in such a manner that the majority of the fibres are aligned parallel to the. ylength of the mold. When a fibrous mass or slurry flows under force, the fibres will tend to be aligned in a direction that will reduce the apparent viscosity of the mass to a minimum value; that is, the friction V4or drag between the layers of the vmoving mass will be minimized by the fibre alignment. In fiowing through a pipe the fibres will be aligned so that the fibre lengths will be parallelto the direction of fiow. If the yslurry is run into a mold from a spout or pipe nozzle in a direction perpendicular to the bottom of the mold, the mass will roll out toward the ends of the mold under the previously deposited layer Vof material. This action aligns the fibres concentrically around the point of entry. Hence the majority of fibres will be parallel to the width of they mold. This alignment is undesirable. A much better fibre alignment can be lattained by a filling method as shown in Fig. 8 of the drawings. The slurry 48 is 8 high along both sides near the middle of the mold but drops Volf rapidly in all directions so that the average impact value over the entire block is 11.8 foot-pounds. Fig.

10 of the drawing clearly illustrates the advantage in filling by the preferred direction illustrated in Fig. 8. The highest impact is near the very center of the mold and drops off rather slowly in all directions so that the average impact value over the entire block isV 16.1 foot-pounds.

' VAfter the molds are filled a smoothing roll or scraper may be employed, if desired, to produce a level surface within the molds.

During the mixing and mold filling operations, air pockets are unavoidably trapped in the mix. It is desirable to remove this air since it will leave holes in the finished product. These holes reduce the insulating value and the strength of the units and, where they show, they detract from the appearance of the product. The air can be removed after filling the mold, by means of a vibrator 35, Fig. 2. The ease of removal of air depends upon the viscosity or the apparent viscosity of the liquid slurry. I have emphasized the desirability of a thin suspension both for ease of pouring and for removal of undesirable air pockets. The mass may be vibrated by use of an internal vibrator, such as is used in placing concrete, or the entire mold may be vibrated by any suitable mechanical means.

The mass is then caused to set in the autoclave 36. This takes pla-ce most favorably between l0() and 160 pounds per square inch pressure of saturated steam. The time of setting depends on the reactivities of the lime and the silica, the ratio of silica to lime in the mix, and the degree of completion of the desired reaction. These factors as well as the time of autoclaving, are limited by economic considerations so that the range of autoclaving time will ordinarily vary between 2 and 20 hours.

The total time in the autoclave will exceed .the actual autoclave reaction time at full pressure by 3 or 4 hours.

allowed to strike the bottom of the mold 49 at an angle and near one end. The force of the slurry tends to prevent'a rolling action and to retain the fibre direction Y parallel to the stream movement which is parallel to the length of the'mold. Hence the fibres will be oriented in the preferred direction. The drawing of course illustrates only one means of retaining the preferred fibre orientationestablished in the flow stream. As indicating the results of thev aforedescribed fibre reenforcement, the following example may be cited:

Molded blocks about 36 x 6 x 6 inches were sawed to 4 smaller blocks V36 x 6 x 11/2 inches in such a manner that the saw cut was vertical with respect to the blocks, position when in the mold.V Each smaller block was then cut to 6 x 6 X136 inch pieces which were subjected to an impact test such that the plane of the broken cross section Was perpendicular to the 36 inch length of the original block. The impact tester is of the pendulum type, with a hammer having a striking face 6 x 1% inches, a striking velocity of 8.3 feet Yper second and a capacity to deliver' 28 foot pounds of work. The 6 x Y6 x 11/2 inch test specimen is clamped vertically ina vise with a free end 3 .x 6 x l1/z inches, above the vise. The hammer strikes the piece with a clearance of 1A; inch above the top'of the vise, and the energy absorbedin fracturing the piece is determined. With average impactsY of the pieces from a number of36 x 6 x 6 inch blocks, Va contour diaings is Vsuch a diagram illustrating the variation in re- Venforcing power of the fibre when the mold was filled from a nozzle in a direction perpendicular to the bottom of the mold. It will be noted that the impact value is VThis time is lconsumed in building up-and releasing the pressure.Y It is preferable to build up the pressure rapidly, and at no time before the mass has set should the temperature within the mass exceed the boiling point of water under the particular pressure at that time. Some- Ywhere around one-half or one hour will elapse from the time the pressure is first applied before the Whole mass has reached a sufiicient temperature andV any appreciable setting has occurred throughout the mass. Decreasing the pressure in the autoclave must be done slowly. The rate depends upon the exposed area of the product in relation to'its volume and the volume of Water in the product, As the pressure is released, Vthe temperature of the water in the set mass begins to exceed the boiling point of water corresponding to the particular pressure at that instant and as a result it boils until the excess heat has been consumed. This process, continued until all the pressure has been released, will remove about 2O to 40 per cent of the water. This is a considerable amount of water to move through the microscopic poresV the set pieces removed by the mold stripper 37. This may be a mechanical device to remove the wedges, invert the molds and tap them lightly so as to dislodge the pieces and allow them to drop free from the mold. The molds are then cleaned at 38. This may be done by'a rotating wire brush, or by blasting the mold with a high velocity water jet or with small pellets in an air stream to dislodge any particles of the insulation that are still sticking fast. Y Y

As previously described, parting compounds may be used to eliminate the tendency of sticking to the molds and lubricate the piece in sliding out of the molds. The cleaned molds can be coated in the applicator 39. This may be an oil bath in which the molds are dipped, the excess oil being allowed to drain off. Another means of applying the parting compounds is by spraying or brushing. This may be used for oils, greases or waxes. The greases or waxes can be applied in a liquid state either by heat or solvent. The cleaned and coated molds are now ready for return to the mold filling device 34.

The pieces of set insulation taken from the molds are placed in the drier 40. Many driers of suitable type are available in the industry. The essentially dry pieces are then trimmed at 41 to remove all unevenness.

It is more economical to mold several blocks as a unit and split these to the smaller size blocks. This requires fewer molds since several smaller blocks and blocks of various thickness can be obtained from one large size mold. The splitting operation can be done simultaneously with the trimming process. Any suitable equipment familiar to the industry can be used for trimming and splitting. Examples of such equipment are band saws, circular saws and milling cutters. The waste and trimmings may be discarded as at 42 or pulverized as at 31 and a portion returned to the system for reuse as described above. The trimmed pieces are ready for packaging 43 and shipment.

The process described above is merely illustrative and not intended to limit the scope of the invention, since variations in the process are possible without departing from the spirit of the invention. For example, the pulverized insulation waste may if desired be left out of the composition; the order of mixing the raw materials may be altered; all silica sand or all diatomaceous earth may be used instead of the combination; dry hydrated lime may be substituted for the freshly hydrated quick lime; variation in the fibre type and fibre preparation may be utilized; and trimming may be done before drying instead of after drying.

While it is considered that the reaction between calcium hydroxide and silica affords the best results in production of thermal insulation of the character described, it is to be noted that other alkaline earth compounds may be employed and also other suitable siliceous and aluminous materials. The alkaline earth compounds may be any suitable substance capable of liberating alkaline earth hydroxides with water and thereby capable of reacting with the siliceous or aluminous materials to form a cementing bond. Magnesium hydroxide, for example, when reacted with a highly reactive silica in the form of a natural diatomaceous earth in a procedure and in relative proportions corresponding substantially with those herein described, afforded a magnesium silicate product of adequate but substantially lower modulus of rupture-to-density ratio than that of the corresponding calcium silicate product. The products afforded under like conditions by the hydroxides of barium and strontium exhibited still lower ratios of modulus of rupture-to-density, showing decided advantages in the use of calcium. Examples of calcareous materials that may be used as a raw material in the practice of this invention are quick lime, wet or dry slaked lime, Portland cement or the like. It is preferable that the alkaline earth materials be in a very tine state of subdivision before the reaction is caused to occur.

The siliceous raw materials may be any substance containing silica that is capable of reacting with alkaline earth hydroxides to form a bond. Examples of such materials are silica sands, silica gels, diatomaceous earth, pozzuolana or the like. Diatomaceous earth is of particular value in that through its use the thermal conductivity may be somewhat reduced as compared to that when pulverized silica sand is used.

The aluminous raw materials may be any substance containing alumina that is capable of reacting with alkaline earth hydroxides to form a cement bond. Examples I of such materials are bauxite, any hydrated aluminum oxide extract of bauxite, clays or the like.

The reaction between the alkaline earth hydroxide and the siliceous or aluminous materials require the presence of water. The exact mechanism of the reaction to form a set condition is not understood. The theory is that the reaction between lime and silicia occurs by the precipitation of a hydrated calcium silicate. Evidence seems to indicate that a pentita-hydrate of a mono (meta) calcium silicate is formed. The Water is needed then to form the solutions necessary for the reaction, in addition to composing a part of the reaction product. Water is also required to maintain the desired void space. The weight of water may vary between 3 to 10 times the weight of the dry, raw materials depending upon the density desired in the iinished product. The iinely divided solids must be held in suspension and in a dispersed condition. This is accomplished by the use of the prepared asbestos iibres, as set forth above.

The reaction stated above will take place to a limited etxent at room temperature. For practical reasons the speed of the reaction is increased considerably by subjecting the mixture to higher temperatures in the presence of water. In order to attain the conditions of temperature and moisture, saturated steam under pressure is required. This autoclaving process also elects a more complete reaction between the alkaline earth hydroxide and the siliceous or aluminous materials. It has been found that the gerater the conversion of all the raw materials to the cementing bond, the better will be the strength and stabiliy of the final product. In order to get the highest degree of transformation a balance must be held among the separate variables. These variables include autoclaving time, autoclaving temperature, degree of neness of the reacting materials and the ratio or" the silica or alumina to alkaline earth hydroxides.

The ratio of the mols of silica present in the siliceous materials to the mols of lime present in the calcareous materials, may vary between 1 and 3, depending upon the desired properties of the product, the reactivity of the l raw materials, and the time and temperature allowed to autoclave the mix.

The effect of some of the variables are shown graphically in the curves of Fig. 11 to Fig. 22, inclusive.

Figs. 1l and 12 show the variation in physical properties of a particular composition when the amount of mixing water is altered. This change in mixing water, of course, atects the density which is the value plotted. These curves are typical of the materials and although they were made from one particular set of conditions, nevertheless they show the general tendency of the material under other conditions. They show what rate of increase may be expected for the hardness, transverse strength, compressive strength and abrasion resistance by an increase in density.

Figs. 13 and 14 exemplify the changes in physical properties when the composition of the silica and lime is varied.

Figs. 15 and 16 show the change in some of the physical properties when the composition of the silica and the lime is varied. These curves differ from those of Figs. 13 and 14 in that the range of silica to lime ratio is much more limited in Figs. 15 and 16, also the degree of reactivity of the lime was greater than in Figs. 13 and 14, and the transverse strength has been expressed as a ratio of the modulus of rupture to the square of the density. This was done to eliminate the density variable, and the expression is permissible since the modulus of rupture to density ratio shown in Fig. ll varies as a straight line function of the density and will intersect zero transverse strength at Zero density. A third variable, autoclaving time, is introduced in the curves of Figs. 15 and 16.

Fig. 17 exemplifies the elect of the type of silica used as a raw material on the thermal conductivity of the product.

. in these tests was autoclaved aboutV 16 hours.

Y otherwise detrimental impurities.

Fig. 18 illustrates the effect of iineness of the silica on the strength of the product at various autoclaving times.

Fig. 19 repersents the reenforcing effect of thel fibres expressed as the function of density and impact strength as related-to shippability.

Fig. 20 shows another method for evaluating the reenforcing effect of the fibres. 'Y Y Fig. 21 shows the result of the degree of lime reactivity on the strength of the product when subjected to ditferent autoclaving times, Y

Y Fig. 22 .represents the change vin physical properties of the dried product after exposing it to moist carbon dioxide gas as compared toV theproperties before exposure. An excess of lime in the Vproduct impairs some of the physical properties. This condition is shown to anA exaggerated extent' by the rather severe test exemplied in Fig. 2.2.V The calcium silicate product used By refern'ng tothe curves in Fig. l5 it will be noted that in 16 hours the maximum strength occurs using a mol ratio of silica to lime of about 1.35. In Fig. 22, the properties are noted to change appreciably below a ratio of 1.35. This .indicates that the products made with a silica-lime ratio less than those ratios corresponding to the maximum strength. at one particular autoclaving time, may contain free lime. In order to insure against -the presence of free lime, the original hydrated lime should be in a tine state of sub-division; that is, the calcium hydroxide particles should have nearly colloidal dimensions so as to be highly reactive besides contributing to the suspending actionY of the asbestos libres.

Probably its activity depends on the many lsurfaces avail- Vable to react and on the colloidal nature of the lime forming aV dispersesuspension so that allsurfaces arev ymore readily available for reaction. Y n

` The effect of autoclaving time on the strength of theV 1 product using two limes of different degrees of activity is shown in Fig. 21.V The Strength is a result of the Ydegree of completion of the reaction.

Y v The poorly reactive lime produces weaker material; the result of a less complete reaction. YSome ofthe lowered strength of the less reactive lime may also have been a result ofV a greater amount of impurities particularly calcium carbonate since this lime was a dry hydrate. Y

' ln-the practice of this invention, it is believed that the use of hydrated quickVV lime gives the best results because it introduces a minimum of non-binding or It has been found that a very highly colloidal and highly reactive calcium hy- Ydroxide can be prepared most readily by the ,use of socalled pebble lime. The hydration is accomplished by using an excess of Water. retical weight of water to form calcium hydroxide is used, or approximatelyY six times the Weight of the pebble lime. The best colloidal dispersion of the calcium hydroxide is formed by a rapid means of hydration. speed of the hydration can be increased by a more vigorous agitation and/or an increase in hydration tempera- Vture. The choice of the proper quick lime also has abearing on its speed of hydration. In the parlance of the lime industry, an immediate-'slaking lime is preferred. The poorlyrreactive lime shown in Fig. 21 wasY Y hydrated with only a slight excess of Water so that m- Vsurface of the block acquires a tensile stress and the AboutV twenty times the theo- TheV The critical lengthV other surface a compressive stress. Since the product has a compressive strength considerably iniexcess of its'- surfaces is great enoughvto exert a.force on the libresV It has been Vfound that harsh iibres are advantageous in thisrrespect..

of suicient magnitude Ato pullthem apart.

A harsh fibre is one that has aconsiderable degree of resiliency, such that a deflected-fibre will return tol its originally straight .form upon-removal of lthe'restlaining force.

amphibole group, the harshy Arizona chrysotiles, theV Examples of such fibres are amosites of the harsh African chrysotiles andthe like. Distinguished from them are the soft fibres that can be twisted or bent in any direction and remain essentially inthat position when relieved of the deflecting, forceV such as the Canadian chrysotiles.

Y yDue to the resiliency of the harsh iibres, they can be opened to a suiiicient degree, without exceeding their crictical length to Adiameter ratio, and still yield a good bulk value and thereby supportthe solids in the suspension. be pulped a considerable amount 4to give the necessary bulking value so that the chance, of exceedingV their critical ratio is increased, as isr noted by the broken bres over arruptured cross-sectionof lthe material. The impact strength has been citedrpreviously asa measure of the reenforcing `value ofithe fibres in the i product. Fig. 19 of the drawings,1illustrates therelect that the impact strength has in preventing damage -byV shock in shipment. The data for this curve was obtained from a simulated Vshipping test of the blocks of insulation in cartons.

with the degree of the treatment, nevertheless it does show the trend that can beY expected. The factor (P) represents the per cent ofthe Yblocks that were damaged. If the density is considered as remainingconstant,l then the amount of damage'varies inversely as the impact Y strength, (I) in the drawings.V vIt will alsov be noted` from the drawing4 that to maintain a constant Yper cent damage under a given Ytreatment (P is constant), the

impact must varyas the square of the density. Hence ously, to eliminate the variability of transverse strength induced by the density, the strengthv isaexpressed as the,

ratio of the modulus of rupture to the square of the density.

A ratio of impact strength lint foot-pounds.) to density (inri'aoundspercubic foot) squared Vofr0.l0 will result,V

from Fig. 19,'in a calculated vbreakage of 16 per cent,

while per cent breakage corresponds to a ratio of.l

about 0.05. Hence a materialr having poor 4reenforrcement Will have ratios between 10.05 and 0.10. A better. means of distinguishing the reenforcing'value ofweakerl materials is Whatl' have called the ratio of (fall-backto` break). The break is obtained'as the load to cause rupture by the standard ilexure test.V As soon as the speci-v men breaks, the deflection or'movement of the load ap-Y plying bearing at the mid-span is discontinued and the residual load the specimen' supports is determined. This valueis called the fall-back load'. VThe ratio ofthe:fa1l-.. back load tothe breaking load is shown in-Fig'. 20, asa

function of the ratio of impact to density-squared. It

In Vcontradistinction, soft asbestos fibres must.

O f course, the per cent of damaged blocks represented is only relative and will varyV 13 will be noted that in the region of impact ratios between 0.05 and 0.10, the ratio of fall-back to break is a more sensitive expression.

The following illustration serves to show the reenforc- The above table shows that the reenforcing value of soft fibres is rather low and cannot be distinguished among themselves by the ratio of the impact to density squared. However, the fall-back to break does show a pronounced difference. Fibre grades are classed according to the Canadian Box Test such that the average fibre lengths of a particular grade are classified by numbers, the lower number representing the longer grade. Each class is sub-divided and each sub-division indicated by a letter following the class number. The data above shows that longer fibres and a higher percentage of fibre content has a beneficial effect upon reenforcing the product, but as pointed out, only to a rather small degree.

The value of harsh fibres is best shown by the fol- *A slightly better fibre orientation due to method oi' filling.

The reenforcing power of the fibre is best illustrated in the above table by the ratio of impact to density squared, since above a ratio of 0.10, this expression is the more sensitive one as will be noted on the curve of Fig. 20. Replacing part of the soft fibres by the harsh fibres has a decided beneficial effect. However, the reenforcement is still not quite enough as judged by a comparison to the commercially satisfactory product, 85 per cent magnesia. Complete replacement produces a very satisfactory product that has sufficient reenforcement.

Another means for evaluating the advantage of the harsh fibres can be observed by subjecting full size, commercial pieces to a hot surface and, after cooling, examining the blocks for complete breaks or serious cracks. Pieces 36 x 6 x 11/2 inches were placed on a hot surface, in a stack 4 such pieces deep, at 1530 degrees Fahrenheit for 24 hours. The following table shows the average results of a number of such tests:

A much better reenforcing action of the harsh fibres is evident by examining the results of the hot plate applications given in the above table.

As has been explained previously, several factors are responsible for the increased reenforcement of the harsh fibres; the resiliency and the better length to diameter ratio. However, this advantage is not fully realized unless the fibres are oriented in the preferred direction as has already been set forth. It is believed that the resiliency of the harsh fibres is responsible for the greater ease of proper orientation.

As a mold is filled the slurry tends to roll along, producing minor disturbances in the ilow pattern, probably so-called eddy currents. Soft fibres tend to roll up with the slurry into a ball more-or-less, or to line up parallel to the mold width and in either case to reduce its maximum reenforcing power. Harsh fibres, due to their resiliency, are not influenced to as great an extent by the small eddying movements of the slurry, particularly if the slurry moves forward from the filling nozzle at a relatively high velocity and strikes the bottom of the mold at an angle and near one end. This description is merely by way of explanation for whatever phenomena is responsible and is in no way intended to limit the scope of the invention.

Calcium hydroxide reacts with silica to produce a hydrated calcium silicate. The hydrated calcium silicate formed is in a gelatinous condition. When a particle of siliceous material reacts, a shell is believed to form around the particle preventing, at least for a time, more lime from reacting with the particle to convert it completely to the calcium compound. Thus, if large particles are present they may have unreacted cores in the finished product. These cores add weight to the final product,

but are not microporous and do not contribute to the cementing bond. The result of this condition on the strength of one mix using pulverized silica sand and at different autoclaving times is shown in Fig. 18. The strength of the material containing the coarser sand approaches that of the finer sand on continued autoclaving. This shows the slower reactivity of the coarser sand. Therefore, it is preferable that the silica should be pulverized to as fine a degree as is commensurate with the economy of the process. The structure of the silica molecule is also a factor that controls its reactivity. For example, a hydrated silica such as an opaline silica, is more reactive than a pure quartz silica. Diatomaceous earth is an opaline silica and will react more rapidly than finely pulverized quartz silica. This is due partly to the high surface area of the diatoms. But a calcined diatomaceous earth which has lost its water of hydration, reacts more slowly than uncalcined earth. The hydrated character has some bearing on the speed of the reaction.

I have found another vadvantageous use for the naturally occurring diatomaceous earth. By its use a more eficient thermal insulation is possible. This is shown in Fig. 17 where the thermal conductivity is expressed as a function of the mean temperature of the insulation. The product made with all the silica in the form of diatomaceous earth (curve No. 4) is 20 per cent more eiiicient than that made with all pulverized sand (curve No. 1). As much as 54 per cent of the silica in the form of pulverized sand and the remaining 46 per cent as diatomaceous earth (curve No. 3) may be used Without appreciably lowering the efficiency from that using all diatomaceous earth. The phenomena responsible for the lowered conductivity of the diatomaceous earth mixes are not understood. It is possible that due to the extremely fine condition of the individual particles, they can spread out between the water filled voids to a greater extent so that when the calcium silicate reaction occurs the gelatinous hydrated calcium silicate formed has a finer microporous structure.

The diatomaceous earth is also desirable for its high bulk value. However, several disadvantages present themselves by its use that tend to limit the amount that is used.

perature limit of the product. Hence, in view of the above Y properties, it is desirable to limit the diatomaceous earth so that its silica content is between and 66 per cent of the .total silicainthe mix available for reaction. In

a mixture of diatomaceous earth and pulverized silica, the earth -would lbe about to V80 per cent of the mixture.

According tothe literature, formed calcium silicate gel tends to iillall available space. Therefore, iiner materials, tending to reactmore completely, till the voids between the fibres more completely. When this product dries, its structure will be more highly microporous. Also this structure should have a better crushing strength and will add to the thermal insulating value of the finished.' article.

Another advantage will accrue by the use of very iine particles of raw materials. A light weight body requires a high percentage of void space. In order to attain the necessary voids, the unreacted materials must be held in a dispersed suspension until the cementing bond has formed. The prepared fibre remains fairly well suspended in the necessary dilution by itself. However, when theV lime and the silica are mixed with the bres, they tend to weight down'the fibres, packing the mass to a greater density. This inclination to pack always results in a greaterV tendency to pack toward the bottom of the mass,

impartingV a gain in density with increased depth. It isA desirableto alleviate this condition. It has been found that this can be achieved by the use of iner'materials.

Essentially all particles have some electrical chargesY on,`

their surface. The greater the surface per unit weight, the moreV will be the electrical charge for a unit weight of material. The electrical Vcharges on each particle tend to repel otherparticles of like charge.. It'is felt that this repulsion'assists in supporting the particles in suspension.

' It is preferable that the pulve'rized sand be fine enough so that Vat least '95 per cent will pass through ya standard N o. 200 screen, and at least per centwill pass through a No. 325screen., The diatomaceous earth should be fine 'enough so thatthe residue on a standard No. 200 screen does not exceed 5 per cent. The hydrated lime should have a degree of'lineness such that a slurry of one ypart ofjhydrated limeV in four'partsof water by weight will settle less than one Vper cent of the slurryv height in a ,column 3.6 centimetersV in Vdiameter and 25 centimeters high.

. Not only is the time of setting dependent'upon th reaetivities of Vthe lime and silica, but' on the ratio of the mols of silica tothe mols of lime. Figs. 13. andY 14 show the .relation between some of the physicalproperties of the vset product for a wide rangeof ratios. This sion loss, compression and modulus of rupture are indications of the strength. All three curves show a maximum strengthjatthe same silica-lime ratio. VThis means Vthe most complete reaction for the particular Vconditions Yof Below a ratioof one, the density increased tremendously.V

This may'be due in part to a tendencyV toward settling, but'thejmajorsource.r of this increase is the result of drying shrinkage caused by the weak structure as a resultY of an yexcess of free lime.

. material was prepared from a poorly reactive lime and autoclaved for about 16 hours. The three curves, abrafV ing the maximum strength at 16 hours with that prepared. from a poorly reactive lime (see Fig.` 14), it will beV seen that the maximum strength occurs at a lower silicalime ratio 'for the highly reactive lime and the strength in the latter case is higher. It will be noted that the transvserse strength in Fig. 15 is expressed as the ratio of the modulus-of-rupture to the squarevof the density. This was done to eliminate the variation introduced by differences in density and has been shown previously to be permissible. FromV Fig. 15, as the'autoclaving time is increased, the maximum strengths increase in value and they occur at lower ratios. The silica-lime ratio, having the Vgreatest strength for a particularV autoclaving time, seems to approach a value of one as the autoclaving time is increased without limit.

The elfect of an excess of free lime on the temperature limit of the Vproduct made using pulvcriz'ed silica sandV was determined'by shrinkage measurements on specimens subjected to a soaking heat and is shown in'Fig. 16. The alumina content of the products of this test was low and hence these curves do not strictly apply to those products made with diatomaceous earth as a raw material because of the introduction of a higher aluminacontent. The eiect of alumina in reducing the temperature limit of the product will be explained later. As shown in Fig. 16, an excess of free lime reduces the temperature limit considerably. However, an'excess of free silica reduces it only slightly. It will be noted, also, that the lower the silica-lime ratio (above a value of l), the longer the autoclaving time to produce an equivalent temperature limit. Y

'Based on the desired properties of the product and limited by economic considerations, the time'of autoclaving may vary between 2 and 20 hours at full pressure. 'Ihe slurry of raw materials is caused to set by autoclaving. As explained previously, the' lime reacts with thek silica in the presence of moisture to form a hydrated calcium silicate. This reaction is accelerated by heat (autoclaving). The higher the` temperature, the faster the reaction proceeds. Above a certain temperature, the reaction products diier; more complex hydrated calcium silicates are formed. These are undesirablev because they do not form as good a cementing bond as the simpler compounds formed at the somewhat lower temperatures. The most desirable product occurs at temperatures'between about 328 and 363 degrees Fahrenheit, corresponding to and pounds gauge pressure of saturatedrsteam.

The general theory of the mechanism of setting is the formation of a rigid, irreversible gel. Solutions of lime and silica reactV to form a solution ofk calcium silicate.` EventuallyY a supersaturated solution forms. The precipitation of the hydrated calcium silicate from the super'-r about six to eight Vtimes that in the bag. By a visualw examination, this preparation still retained a considerable quantity of fibre lengths about equal to that of the.l

original bre. They had'considerableresiliency'when pressed in a tight ballgand although large ,bundlesV of fibre had been opened yet the opening was not excessive since a number of tine splits were still present.

Twenty-one and one-quarter pounds of a high calcium, pebble quick-lime were hydrated with three and one-half pounds of pulverized reclaim in iifteen gallons of water. The hydration was carried out under vigorous agitation in a three foot diameter commercial Hydrapulper having an impellor velocity of about 750 revolutions per minute for a period of ten minutes. To the hydrated slurry was added an additional forty-two gallons of water, fteen pounds of the previously prepared amosite bre, nine and three-quarter pounds of 200 mesh pulverized silica sand and twenty-one and one-quarter pounds of a natural diatomaceous earth. This mixture was thoroughly dispersed with high speed agitation using the Hydrapulper for a period of five minutes. 'I'he slurry was then dropped to a cone bottom storage tank from which the lubricated molds were filled. The slurry issued from a pipe at the bottom of the storage tank and hit the bottom of the mold at a forty-tive degree angle at the near end. The mold was vibrated to release any entrapped air pockets. The mold, with its substantially air free contents, was placed in an autoclave. Steam was applied and brought to a gauge pressure of 125 pounds in a matter of about l minutes. Full pressure of 125 pounds was held in the autoclave for 12 hours, whereupon it was released at a uniform rate of pressure decrease and brought to atmospheric pressure in 31/2 hours. The set material was removed from the mold, trimmed and split to smaller sizes. These sized pieces were placed in an oven until thoroughly dried. The average properties obtained are shown in the following chart, in comparison with two of the better commercial insulations of the same general type:

Commercial Insulations of Same General Type Calcium Silicate No. 1 No. 2

Density, pounds per cubic foot 12. 4 22. 5 10. 0 Hardness, millimeters penetratiom'of l/g" ball point under 1 kilogram load- 0. 80 0. 75 0.95 Modulus of Rupture to Density, Ratio. 4. 5 3. 5 5. 0 Impact to Density Squared, Ratio..-" 0. 12 0.12 0.15 Fall-back to Break, Ratio 0.78 0.65 0.75 Compressive strength, pounds per square inch, at 5% reduction in thickness 90.0 95.0 72.0 Abrasion Resistance:

Percent loss in minutes 30.0 35. 0 16.0 Percent loss in 20 minutes 50. 0 60. 0 32. 0 Thermal conductivity, B. t. u. per hour per square foot per degrees Fahrenheit per inch at a mean temperature of:

300 degrees Fahrenheit 0.44 0.65 0.47 800 degrees Fahrenheit 0.80 0. 75

Change in properties after 6 hours soaking heat at degrees Fahrenheit 550 1, 500 1, 900 1, 500

Percent linear shrinkage 0. 2 1. 0 4. 2 1. 9 Percent loss in weight 14 9 9 9. 7 ar ess 1.0 .90 0.55 1.00 Temperature limit, degrees Fahrenheit. 600 1, 900 1 500 In almost all insulation industries, a certain amount of trimmings and rejected materials are obtained. This material is largely waste. It is usually reincorporated as much as possible to otset the loss. In some insulations, particularly 85 per cent magnesia and the clay-bonded, diatomaceous earth products, the waste material tends to increase the density and drying shrinkage without an equal gain in strength. On the other hand, 1 to 10 per cent of the finely pulverized, previously formed and dried calcium silicate insulation was found to impart the desirable property of a rather thin and yet stable suspension. A thin suspension is desirable because it is more easily mixed and handled, and any entrapped air may be more readily dislodged.

Fig. 24 shows the etect on a calcium silicate product,

prepared lin the hereindescribed manner, of different per'- centages of added reclaim. With no reclaim the batches were rather thin, and settling of the solids in the mold was appreciable. The tendency to settle becomes progressively less with increasing percentages of added reclaim, but since the modulus of rupture-density ratio is also progressively reduced the practical limit appears to be in the neighborhood of 25 per cent since beyond that point the aforesaid modulus of rupture-density ratio tends to fall below the established minimum for products of this character. In general, it is preferred to use the reclaim in amounts in the neighborhood of 5 per cent as indicated for example, in the following formula:

21.2 per cent asbestos fibre 30.0 per cent CaO 30.0 per cent natural powdered diatomaceous earth 13.8 per cent pulverized silica 5.0 per cent reclaim.

It is well known that the fusion point of any pure substance is nearly always reduced somewhat by the addition of small amounts of impurities. For an insulation, the reduction of the fusion point also means a lowering of the useful temperature limit of the material. It has been found that such is the case with calcium silicate insulation. Small percentages of iron impurities reduce the temperature limit somewhat, but small percentages of alumina were found to be particularly detrimental in this respect.

If small pieces of insulation, say 5x2xl inches in size, are subjected to soaking heat tests for a period of at least 6 hours, there will be a soaking temperature above which the shrinkage becomes excessive and numerous cracks develop. It has been observed that this temperature corresponds to an average linear shrinkage of about 4.5 per cent. For the sake of brevity, this will be called the temperature limit of the material in the following discussion. It is not, however, to be confused with the true temperature limit, mentioned previously, of the full size insulation applied to a hot surface. This latter limit is always lower than the former. The difference between them is a function of the effective fibre reenforcement within the material.

In order to clarify the role of these impurities in calcium silicate insulations, some test results are cited below. A chart, Fig. 23, reveals graphically the eect of the alumina content on the reduction of the temperature limit. All the alumina contents cited below and in the drawings are free alumina contents (that yconf tent available for reaction with the lime) in addition to that of the basic mix used for this series of tests. The basic mix is composed of a molar ratio of silica to lime of 1.4 using 12 per cent chrysotile fibre and pulverized silica sand, and which consists of an approximate initial free alumina content of 0.7 per cent.

Five per cent iron oxide, added as very nely powdered red ferrie oxide reduced the temperature limit from 1900 to 1750 degrees Fahrenheit. However, tive per cent alumina, reference 1 in Fig. 23, added as very finely powdered bauxite, reduced the temperature limit from 1900 to 1400 degrees Fahrenheit. Ten per cent alumina, reference 1 in Fig. 23, was no more effective than live per cent. A mixture of five per cent alumina and five per cent ferric oxide, reference 4 in Fig. 23, had a limit around 1350 degrees Fahrenheit, while one having 21/2 per cent alumina and 21/2 per cent ferrie oxide, reference 4 in Fig. 23, had about 1450 degrees Fahrenheit as a limit.

A calcium silicate prepared using portland cement as the lime-producing ingredient, introduces alumina, reference 2 in Fig. 23. The composition of the lime and silica when held constant in the finished product, but made with varying amounts of lime, pulverized silica sand and Portland cement reduced the temperature limit from 19,00 degrees F ahrenheitto about the following values:

Percent'Portland Ce-VV Approximate percent T Y ment; in the Raw A1203 introduced in emperature 1mm?, Materials Product Degrees Fahrenheit When 15 per cent bentonite clay, reference 5 in Fig. 23, 'Y

was vadded with the raw materials so that the nished chemical analysis was Vpractically unchanged except for an increase of l3 to 4 per cent in the alumina content.

the temperature limit was reduced from 1900 to about Y 1400 degrees Fahrenheit.

Diato'maceous earth, reference 3 in Fig. 23, as a 4sourceof silica, ,whoseV content in the insulation was around 50 percent, introduced 1%. to 2 per cent alumina above that which was introduced by'usingfairly pure pulverizedvsilica sand. Thetemperature limit was reduced from 1900 to a value between 1600 and 1700 degrees Fahrenheit.

As stated above, the material prepared for this series of tests had an available alumina Vcontent in the finished productof about 0.7 per cent. In order to have a product with aV temperature resistance above 1500 degrees Fahrenheit, an'extra available alumina content of 2.3 per cent, or a total available alumina content of 3.0 per cent of the dry nished product is the maximum permissible. By referring to Fig. 23 it will be apparent that the extra Vavailable alumina content must be limited to 2.3 per cent'tofobtain a temperature limit above 1500 degrees Y Fahrenheit.

The problem is to maintain the total available alumina content below 3.0 per cent. This can be done in several ways. One method` is to use'raw materials having a very VVlow alumina content; either low in alumina originally suchfas high purity pulverized silica sand or hydraulic cements low in alumina; or in which the alumina content is reduced, such asaby washing clay materialsV from diatomaceous earth. A second way is to use Vonly limited quantities of materials higher in alumina suchas clays, portland cements, kdiatoma'ceous earths, etc., so as'to keep Y theV available alumina content of themix below 3.0 per Y cent on the basis of the nished product.

If itisV desired to maintain the temperature limit in excess of 1700 degrees Fahrenheit, the maximum extra, available alumina content allowable would be 1.2 per Y cent, or a total, maximum, available content of 1.9'per cent. This is evidentffrrom Fig. 23. Likewise, a total,

Cit

20 maximum,'available alumina `content of 1.3 per cent'is'the limit'allowable to maintain a temperature limitabove 1800 degrees Fahrenheit. f-

I claim:

`.1.ln the manufacture of elongated shapesroftliermal Vgated upwardly-open panacastmolds each having avertical cross sectional area greater than that of said discharge orilice by successively positioningneach mold with one end thereof adjacent said dischargeorifice and with'the mold extended therefrom beyond said oricein the direction of Vflow from said orifice, and delivering successive portions of the slurry from the flow line intothe molds, each moldy being retained in the position referred to during the filling thereof, thereby providing for charging of the molds withV charges of the slurry retaining libre orientation imparted to the slurry in the flow line and having said fibre orienta-y tion disposed lengthwise of the molds, and curing the fibre-oriented charges in the molds. Y

2. A thermal insulation comprising a substantially homogeneous micro-porous body elementfessentially consisting of the reaction products of calcium hydroxide and siliceous material together with reinforcing asbestos ibres,

said body having a densityof from 7 to 20 pounds per cubic foot, and the asbestos bre content of said body being from 8% to 40% by Weight of the dry solids Vcontent thereof, and said body containing notV inexcess of 3% reactable alumina and having a temperature resist-y ance such that when a plurality of pieces thereof 11/2'" thick and 6" wide are stacked upon a surface heated to approximately 1550 F., no appreciable cracking of the pieces occurs.

References Cited in the tile of this patent UNITED STATES PATENTS 1,520,893 Teitsworth Dec. 30, 1924 2,326,516 Brown Aug. 10, 1943 2,400,884 Lloyd May 28, 1946V 2,421,721 smith '11111611947 2,432,981 Abrahams Dec. 23', 1947 2,442,519 Schuetz June l, 1948 2,469,379 Fraser May l0, 1949 au.. an t 

2. A THERMAL INSULATION COMPRISING A SUBSTANTIALLY HOMOGENEOUS MICRO-POROUS BODY ELEMENT ESSENTIALLY CONSISTING OF THE REACTION PRODUCTS OF CALCIUM HYDROXIDE AND SILICEOUS MATERIAL TOGETHER WITH REINFORCING ASBESTOS FIBRES, SAID BODY HAVING A DENSITY OF FROM 7 TO 20 POUNDS PER CUBIC FOOT, AND THE ABESTOS FIBRE CONTENT OF SAID BODY BEING FROM 8% TO 40% BY WEIGHT OF THE DRY SOLIDS CONTENT THEREOF, AND SAID BODY CONTAINING NOT IN EXCESS OF 3% REACTABLE ALUMINA AND HAVING A TEMPERATURE RESIST- 